structure to file [REMAIN UNSOLVED] [CLOSED]

jk chan · modified on Saturday, February 19, 2011 9:43 AM

Student st; WriteFile(file,&st,sizeof(st),&written,0); open file using Createfile API, or you can use fopen("file","wb"); and fwrite C run time APIS. is it so complicated? :)

If u can Dream... U can do it

goldenrose9

jk chan wrote:

you can use fopen("file","wb"); and fwrite C run time APIS. is it so complicated?

i know how to read and write using fread and fwrite. But i want my program to use WriteFile() and ReadFile()

Some Day I Will Prove MySelf :: GOLD

goldenrose9

#include <windows.h>
#include <conio.h>
#include <iostream>

using namespace std;

struct Detail{
wchar_t Name[25];
long Age;
wchar_t Address[100];
};

struct Student{
Detail detail;
DWORD code;
};

int main()
{

DWORD BytesWritten=0, BytesRead=0;
Student st,read;

st.code =1;
st.detail.Name = TEXT("Williams");
st.detail.Age = 25;
st.detail.Address = TEXT("B-33 Lane 5");


HANDLE hFile = CreateFile(TEXT("C:\\\\demo.txt"),GENERIC\_READ | GENERIC\_WRITE,0,0,OPEN\_ALWAYS,FILE\_ATTRIBUTE\_NORMAL,0);
if (hFile != INVALID\_HANDLE\_VALUE)
{
	WriteFile(hFile,&st,sizeof(Student),&BytesWritten,0);
	ReadFile(hFile,&read,sizeof(Student),&BytesRead,0);
	CloseHandle(hFile);

	cout<<read.code<<endl;
	cout<<read.detail.Name; 
}
else
{
	cout<<"Error! Cannot Open File";
	exit(1);
}
\_getche();
return (0);

}

when executing this code following error occurs.

Error 1 error C2440: '=' : cannot convert from 'const wchar_t [9]' to 'wchar_t [25]'
Error 2 error C2440: '=' : cannot convert from 'const wchar_t [12]' to 'wchar_t [100]'

Some Day I Will Prove MySelf :: GOLD

David Crow

goldenrose9 wrote:

st.detail.Name = TEXT("Williams"); st.detail.Address = TEXT("B-33 Lane 5");

You probably meant to use _tcscpy() here instead.

"One man's wage rise is another man's price increase." - Harold Wilson

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

"Man who follows car will be exhausted." - Confucius

Alain Rist

Hi,

goldenrose9 wrote:

when executing this code following error occurs.

When compiling is not when executing. 1 You do not correctly initialize your st structure, change to:

Student 
	st = {{TEXT("Williams"), 25, TEXT("B-33 Lane 5")}, 1 },
	read = {0};

2 Your code will then compile but not to your expected result, you must set the file pointer to FILE_BEGIN before reading:

	WriteFile(hFile,&st,sizeof(Student),&BytesWritten,0);
	SetFilePointer(hFile, 0, 0, FILE\_BEGIN);
	ReadFile(hFile,&read,sizeof(Student),&BytesRead,0);

cheers, AR

When the wise (person) points at the moon the fool looks at the finger (Chinese proverb)

goldenrose9

DavidCrow wrote:

You probably meant to use _tcscpy() here instead.

This works like a charm

_tcscpy(st.detail.Name,TEXT("Williams"));
_tcscpy(st.detail.Address,TEXT("B-33 Lane 5"));

But another problem arises cannot set values in long and DWORD variables

struct Detail{
wchar_t Name[25];
long Age;
wchar_t Address[100];
};

struct Student{
Detail detail;
DWORD code;
};

Student st;
st.code = 1;

but st.code stores a default value of -16843010 and same problem with long data type st.Details.Age = 25 stores 65278, instead of 25. :confused: :wtf: MODIFIED: _tcscpy_s() now works. i was making a small mistake. Now it works..

_tcscpy_s(st.detail.Name,_tcslen(st.detail.Name),TEXT("WILLIAMS"));

Some Day I Will Prove MySelf :: GOLD

modified on Wednesday, February 16, 2011 10:43 PM

David Crow · modified on Wednesday, February 16, 2011 10:43 PM

goldenrose9 wrote:

why error is occurring in _tcscpy_s()

Hard to say since you did not indicate what the error was.

"One man's wage rise is another man's price increase." - Harold Wilson

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

"Man who follows car will be exhausted." - Confucius

ShilpiP · modified on Wednesday, February 16, 2011 10:43 PM

Try ZeroMemory

Student st,read;
ZeroMemory(&st,sizeof(st));

I believe in LOVE AT FIRST SIGHT... Bcoz I have loved my Mother... even since I opened my eyes...(ICAN)

Lost User

st.detail.Name = TEXT("Williams");

You cannot copy characters in this way, you must use one of the copy methods.

I must get a clever new signature for 2011.

Niklas L

To OP: This is only meaningful if you don't intend to initialize every member separately.

home

David Crow · modified on Wednesday, February 16, 2011 10:43 PM

goldenrose9 wrote:

i was making a small mistake.

And you still are. _tcslen() does not tell you the size/capacity of Name, but rather how many characters it is currently holding.

"One man's wage rise is another man's price increase." - Harold Wilson

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

"Man who follows car will be exhausted." - Confucius

goldenrose9

yes you are right. but when i use

_tcscpy_s(st.detail.Name,sizeof(st.detail.Name),TEXT("WILLIAMS"));

stack around st get corrupted. moreover when i initialize st with

st.code =1;
st.detail.Age = 25;

then the value is changed to

st.code = 4278124286
st.detail.Age = -16843010

i had intialized the st as given

st.code =1;
st.detail.Age = 25;
_tcscpy_s(st.detail.Name,sizeof(st.detail.Name),TEXT("WILLIAMS"));
_tcscpy_s(st.detail.Address,sizeof(st.detail.Address),TEXT("BB-33 LANE 5"));

Some Day I Will Prove MySelf :: GOLD

David Crow

Have you considered:

st.code = 1;
st.st.Age = 25;
_tcscpy_s(st.st.Name, sizeof(st.st.Name), TEXT("WILLIAMS"));
_tcscpy_s(st.st.Address, sizeof(st.st.Address), TEXT("BB-33 LANE 5"));

For clarities sake, you might consider renaming the st member of Student.

"One man's wage rise is another man's price increase." - Harold Wilson

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

"Man who follows car will be exhausted." - Confucius

goldenrose9

whenever st.code and st.st.Age is initialized with any value the result is,

st.code = 4278124286
st.detail.Age = -16843010

Some Day I Will Prove MySelf :: GOLD

David Crow

You need to look more closely at the code snippet I provided. You should not be assigning or referencing st.Detail. In your Student structure, Detail is a type of structure, not an instance of one.

"One man's wage rise is another man's price increase." - Harold Wilson

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

"Man who follows car will be exhausted." - Confucius

goldenrose9

please give a small example. :confused:

Some Day I Will Prove MySelf :: GOLD

David Crow

See here.

"One man's wage rise is another man's price increase." - Harold Wilson

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

"Man who follows car will be exhausted." - Confucius

goldenrose9

on using

st.code = 1;
st.st.Age = 25;
_tcscpy_s(st.st.Name, sizeof(st.st.Name), TEXT("WILLIAMS"));
_tcscpy_s(st.st.Address, sizeof(st.st.Address), TEXT("BB-33 LANE 5"));

following error occurs.

Error 1 error C2039: 'st' : is not a member of 'Student'
Error 2 error C2228: left of '.Age' must have class/struct/union

Some Day I Will Prove MySelf :: GOLD

David Crow

I just compiled your code with my changes. It compiled and ran fine.

"One man's wage rise is another man's price increase." - Harold Wilson

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

"Man who follows car will be exhausted." - Confucius

goldenrose9

please give a sample so that i can understand my mistake.

Some Day I Will Prove MySelf :: GOLD